NAI Concentration (number/cm3) | Level | Relationship With Health |
≤500 | 1 | Unfavorable |
500 - 800 | 2 | Normal |
800 - 1100 | 3 | Somewhat Favorable |
1100 - 1400 | 4 | Favorable |
1400 - 1700 | 5 | Quite Advantageous |
1700 - 2000 | 6 | Very Advantageous |
≥2000 | 7 | Extremely Advantageous |